Today, for most people, sailing is a hobby.
Sailing can be further divided into two areas: Racing and Cruising.

In ancient times (see Odysseus), ships used following or rear-quarter winds. They therefore had to wait in port or at sea for the right wind directions.

Modern sailing ships are able to go against the wind from an average of 25 degrees relative to apparent wind for most sloop-rigged yachts, to as little as 16 degrees for modern (America's cup type) racing sloops. How close a boat can sail to the wind depends on the wind speed, since what the boat "sees" is the apparent wind, i.e., the vector sum[?] of the actual wind and the boat's own velocity. The apparent wind is what the windex on top of the mast shows. Because of this, people often talk about how close a boat can sail to the apparent wind. A good sloop can sail within 25 degrees of apparent wind. Perhaps an American Cup sloop can sail within 16 degrees, under the right conditions. Those figures might translate into 45 degrees and 36 degrees relative to the actual wind.

Sailboats typically have one, two, or three hulls.
Vessels with one hull are known as monohulls, those with two or more are known as multihulls.
Multihulls can be further subdivided into catamarans (two hulls), and trimarans[?] (three hulls).

Behaviour
Sailors are expected to know the essentials of boating safety which include right-of-way rules, lights, signals and various rules designed to support safe navigation. There are unlimited more esoteric etiquette rules and custom that will demonstrate to others advanced knowledge of boating protocol such as pulling up the fenders when you're not in port and especially safety rules such as ducking one's head when one hears "prepare to come about".

Terminology
Sailors use traditional terms for the parts of or directions on a vessel; starboard (right), port (left), forward or fore (front), aft (back), bow (very front), stern (very back). Vertical poles are masts, horizontal poles are booms (if they can hit you), gaffs (if they're too high to reach) or poles (if they can't hit you). Ropes or wires that hold up masts are called shrouds or stays. Ropes or wires that raise and lower sails are called halyards. Ropes that adjust (trim) the sails are called sheets. Ropes that pull on poles are called vangs. Actually, only a few of the "ropes" on a boat are called ropes.
A few examples, the bell rope (to ring the bell), a bolt rope (attached to the edge of a sail for extra strength), a foot rope (on old square riggers for the sailors to stand on while reefing or furling the sails), and a tiller rope (to temporarily hold the tiller and keep the boat on course). All other material that might at first glance seem to be rope is actually line or rode.

Walls are called bulkheads. The toilet is the head, the kitchen is the galley, etc. Sails in different sail plans have unchanging names, however.
For the naming of sails, see sail-plan.

Sailing terms have entered popular language in many ways.
"Broken up" was the fate of a ship that hit a "rocky point."
"Pooped" refers to the poop deck of a ship, where tired or ill sailors hung their hammocks.
"In the doldrums" referred to being becalmed, windless, especially in the narrow band of hot windless water "the doldrums", near the equator.
"Adrift" meant literally that a ship's anchor had come loose, and the ship was out of control near land and therefore in serious danger.
"Keel-hauled and hung out to dry." was the rather nasty process of attaching a sailor to a rope, and drawing him under the sailboat while underway, and then hanging him from a yard-arm (under his shoulders usually, not by his neck), where officers and crew could mock him.
A "broadside" was the simultaneous shooting of all the cannon on one side of a ship.